<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            border: solid green 5px;
            width: 200px;
            height: 100px;
            /* margin: auto; */
            text-align: center;
            /* margin-left: auto;
            margin-right: auto; */
            margin: 0px;
            padding: 0px;
        }
    </style>
</head>
<body>
    <div>这是一个div</div>
    <div>这是一个div</div>
    <div>这是一个div</div>
</body>
</html>